Today, red dot effect is common in existing invisible-light light-emitting diode chips: during visual observation of chip lighting, it can be seen that some dark red light is emitted from the chip when it is lighted on. This restricts the needs for pure infrared light free of red dots in application. Therefore, it is necessary to provide an invisible-light chip free of visible light in the market.
Referring to Chinese patent No. CN1758457A for an example, a conventional infrared light-emitting diode is disclosed. In this structure, the light absorption layer has a band gap wider than the band gap of the active layer. It is therefore possible to reduce red light components by absorbing the components at the skirt on the shorter wavelength side of the radiation spectrum.